build: ship "_core/*" as bytecode (built-into Nvim binary)

Problem:
We want to encourage implementing core features in Lua instead of C, but
it's clumsy because:
- Core Lua code (built into `nvim` so it is available even if VIMRUNTIME
  is missing/invalid) requires manually updating CMakeLists.txt, or
  stuffing it into `_editor.lua`.
- Core Lua modules are not organized similar to C modules, `_editor.lua`
  is getting too big.

Solution:
- Introduce `_core/` where core Lua code can live. All Lua modules added
  there will automatically be included as bytecode in the `nvim` binary.
- Move these core modules into `_core/*`:
  ```
  _defaults.lua
  _editor.lua
  _options.lua
  _system.lua
  shared.lua
  ```

TODO:
- Move `_extui/ => _core/ui2/`

1 files changed, 0 insertions, 23 deletions

diff --git a/runtime/lua/vim/_buf.lua b/runtime/lua/vim/_buf.lua
deleted file mode 100644
index 0631c96f77..0000000000
--- a/runtime/lua/vim/_buf.lua
+++ /dev/null
@@ -1,23 +0,0 @@
-local M = {}
-
---- Adds one or more blank lines above or below the cursor.
--- TODO: move to _defaults.lua once it is possible to assign a Lua function to options #25672
---- @param above? boolean Place blank line(s) above the cursor
-local function add_blank(above)
-  local offset = above and 1 or 0
-  local repeated = vim.fn['repeat']({ '' }, vim.v.count1)
-  local linenr = vim.api.nvim_win_get_cursor(0)[1]
-  vim.api.nvim_buf_set_lines(0, linenr - offset, linenr - offset, true, repeated)
-end
-
--- TODO: move to _defaults.lua once it is possible to assign a Lua function to options #25672
-function M.space_above()
-  add_blank(true)
-end
-
--- TODO: move to _defaults.lua once it is possible to assign a Lua function to options #25672
-function M.space_below()
-  add_blank()
-end
-
-return M